1. Field
Exemplary embodiments of the present invention relate to a magnetic memory device and an operating method thereof, and more particularly, to a magnetic memory device which uses both the STT (Spin Transfer Torque) effect and the SOT (Spin Orbit Torque) effect to write data, and an operating method thereof.
2. Description of the Related Art
Magnetic memory is one of leading next-generation memory device technologies. Recently, research has been conducted on magnetic memory devices using the STT effect and the SOT effect.
FIG. 1 is a structure diagram of a conventional magnetic memory cell that uses the STT effect.
The magnetic memory cell using the STT effect includes a word line 2 formed over a substrate 1, a drain 3 and source 4 formed in the substrate 1 on opposing sides of the word line 2, and a gate insulating layer 5 formed between the substrate 1 and the word line 2.
The magnetic memory cell further includes a drain electrode 6, a source electrode 7, a metal layer 8, an MTJ (Magnetic Tunnel Junction) element 10, a bit line electrode 9, a bit line 30 and a source line 20. The drain electrode 6 is formed on the drain 3, and the source electrode 7 is formed on the source 4. The metal layer 8, the MTJ element 10, the bit line electrode 9 and the bit line 30 are sequentially formed over the source electrode 7, and the source line 20 is formed over the drain electrode 6.
As illustrated in FIG. 1, the magnetic memory cell occupies an area of 6F2.
The MTJ element 10 includes a fixed layer 11 for which the spin is fixed, a barrier layer 12 and a free layer 13 of which the spin is variable.
The magnetic memory device using the STT effect writes data by applying a current through the MTJ element 10 to adjust the spin orientation of the free layer 13 of the MTJ element 10, and reads data according to a resistance or current difference which occurs depending on the spin orientation of the free layer 13. That is, current flows through MTJ element 10 during read and write operations. A write operation using the STT effect may be referred to as current-induced switching, which is caused by a current that is perpendicular to the layers of the MTJ element 10.
The magnetic memory device using the STT effect uses a large magnitude of current in order to adjust the spin orientation. Thus, while the power consumption of the magnetic memory device is increased, the durability thereof may be reduced by stress applied to the MTJ element 10.
FIG. 2 is a structure diagram of a conventional magnetic memory cell that uses the SOT effect.
The magnetic memory cell using the SOT effect includes a word line 2 formed over a substrate 1, a drain 3 and source 4 formed in the substrate 1 on opposing sides of the word line 2, and a gate insulating layer 5 formed between the substrate 1 and the word line 2.
The magnetic memory cell further includes a drain electrode 6, a source electrode 7, a write line 40, an MTJ element 10, a bit line electrode 9, a bit line 30 and a source line 20. The drain electrode 6 is formed on the drain 3, and the source electrode 7 is formed on the source 4. The write line 40, the MTJ element 10, the bit line electrode 9 and the bit line 30 are sequentially formed over the drain electrode 6, and the source line 20 is formed over the source electrode 7.
At the top of the write line 40 adjacent to the free layer 13 of the MTJ element 10, a spin-hall effect material layer 50 is formed.
In the magnetic memory device using the SOT effect, current flows between the write line 40 and the drain 3 during a data write operation.
That is, current which flows in a direction parallel to the MTJ element 10 through the write line 40 causes a spin-hall effect in the spin-hall effect material layer 50, which causes the spin direction of the free layer 13 to change in a write operation. In other words, the SOT effect changes the state of a memory cell by field-induced switching, where the field is caused by current flowing parallel to the layer surfaces, or layer orientation, of the MTJ element 10.
During a read operation, a current flows through the MTJ element 10 and the drain 3 via the bit line 30. According to a resistance or current difference which occurs depending on the spin orientation of the free layer 13 during the read operation, data are identified.
The magnetic memory device using the SOT effect does not directly apply a current to the MTJ element 10 during a write operation, but additionally includes the write line 40. Thus, the structure of memory cell of an SOT device is more complex than that of cell of an STT device, so the size of a unit cell in an SOT device is larger than a unit cell in an STT device. As illustrated in FIG. 2, the magnetic memory cell using the SOT effect occupies an area of 9F2.
Therefore, a conventional magnetic memory device which perform write operations using the STT effect use large amounts of energy, while a conventional device that uses the SOT suffers from a larger cell size.